JP2556031B2 - SPECT image reconstruction device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a SPECT (single photon emission computer tomography) image reconstruction apparatus, and in particular, a SPECT image reconstruction apparatus that performs absorption correction in the presence of a non-uniform absorber such as when the examination region is the myocardium of the chest. Concerning component devices.

[Prior art]

In the SPECT image reconstruction device, the radiation emitted from the RI (radioisotope) in the subject is absorbed by the absorber inside the body, so it is necessary to correct it. Serenson JA: Quantitative m
measurement of radioactivity in vivo by whole-body
counting.In Instrumentation in Nuclear Medicine.v
ol.2, Hine GJ, Serenson JA, eds.New York, Academic Pres
s, 1974, pp311-348 and Chang LT: A method for attenua
tion correction in radionuclide computed tomograph
y.IEEE Trans Nucl Sci NS-25: 638-643,1978 and Tana
ka E, Toyama H, Murayama H: Convolutional image recon
construction for quantitative single photon emission
computed tomography.Phys Med Biol 29: 1489-1500,19
An absorption correction method that assumes a uniform absorber represented by 84 is known. In addition, the absorption correction method by successive approximation (Budinger 1980) is also known.

[Problems to be Solved by the Invention]

However, the absorption correction method that is usually used is one that performs processing in a uniform absorber space that does not depend on the body surface contour, such as standardized projection (centered projection) based on the RPC method of Tanaka et al. Since it is different from the nonuniform absorber, an error occurs. For example, when the myocardial SPECT image of the chest composed of a non-uniform absorber is applied, this absorption correction method causes problems such as deviation of absolute value, image distortion, and enhancement of hack ground. Although the absorption correction method by successive approximation can solve such a problem, it has a long calculation time and has a problem in practicability. The present invention corrects an error due to a non-uniform absorber by correcting the projection data which has been subjected to the standardized projection by the RPC method with a correction matrix, thereby performing a simple and highly accurate absorption correction. It is an object of the present invention to provide a SPECT image reconstruction device capable of performing the above.

[Means for solving problems]

The present invention is a SPECT image reconstructing apparatus having means for performing a standardized projection process on projection data by the RPC method and image reconstructing means by the back projection method, and a standard RI distribution and absorption at a predetermined examination site. The first obtained by processing the projection data obtained from the body distribution and the standardized projection means.
Of the standardized projection data and the projection data obtained by projecting the image reconstructed using the first standardized projection data again by the standardized projection means to obtain the second standard. Storage means for storing a correction matrix obtained by obtaining comparisons with the converted projection data for each point and each angle; and means for correcting the correction matrix according to the state of the actual examination site of the subject, A means for multiplying the standardized projection data of the actual examination site of the subject obtained by the standardized projection means by the corrected correction matrix is provided.

[Action]

The projection data (sinogram) is obtained by the reprojection process using the standard RI distribution and absorber distribution at the prescribed inspection site of the subject, and standardization projection is performed by the RPC method using this sinogram, and standardization is performed. An image is reconstructed from the sinogram subjected to the projection process by the back projection method. Since the standardized projection processing by the RPC method assumes a uniform absorber that does not depend on the body surface contour, an error is inevitably included due to the existence of the absorber distribution. The sinogram including the error after the first standardized projection processing is C1. Next, the reconstructed image is reprojected on the premise of the absorber distribution to obtain a sinogram again. Then, standardized projection processing by the RPC method is performed on this sinogram. Let C2 be the sinogram after this second standardized projection processing, and this C2 also contains an error because the standardized projection by the RPC method assumes a uniform absorber different from the above absorber distribution. It will be. Here, if a sinogram is assumed to be C0 when it is assumed that the normalized projection according to the above absorber distribution is performed to obtain a sinogram after normalized projection that does not include an error,
The error introduced by the second absorption correction can be expressed as C1-C0. The error caused by the second absorption correction is C2-C1, and the error that is introduced in each of the two absorption corrections is considered to be the same, so C1-C0 = C2-C1. From this, since C0 = 2C1-C2, F = 2-C2 / C1 is obtained, and if F is multiplied by the sinogram processed by the normalized projection by the RPC method assuming a uniform absorber, the error is Can be corrected. Therefore, when the above-mentioned F is obtained for each point and each angle of the sinogram, the correction matrix is obtained and stored in advance, and when the actual projection data of the subject is obtained, first of all, it is uniform. By performing standardized projection by the RPC method assuming an absorber, a sinogram is obtained, and this sinogram is corrected by the above correction matrix according to the actual state of the examination site and then multiplied to obtain a non-uniform absorber. Absorption correction with high accuracy can be performed by removing the influence.

【Example】

In one embodiment of the present invention shown in the figure, the actual subject (patient) to which the single photon-emitting nuclide RI was administered
Projection data (sinogram) for each angle, which is obtained by detecting and collecting gamma rays emitted from, is stored in the data collection memory 1. This sinogram is subjected to a standardized projection process based on the RPC method by the standardized projection device 2, and then sent to the multiplier 5. On the other hand, a standard correction matrix is stored in advance in the correction matrix memory 3, and the correction matrix memory 3 corrects the standard correction matrix according to the actual state of the subject, for example, the central position and size of the myocardium. This corrected correction matrix is sent to the multiplier 5, is multiplied by the sinogram after the above-mentioned standardized projection processing, and is then sent to the image reconstruction processing device 6 to be subjected to superposition integration and back projection processing, and Post-processing by the RPC method is performed to reconstruct the RI distribution image inside the body of the subject. Here, the standard correction matrix stored in advance in the correction matrix memory 3 is obtained as follows. For example, by tracing an NMR (nuclear magnetic resonance) image of a predetermined examination site such as the chest, an RI distribution image and an absorber distribution image are created, and a simulation model of the predetermined examination site is created. As this simulation model, a sinogram obtained by reprojecting the RI distribution image in consideration of the absorber distribution is used. This sinogram is standardized by the standardized projection process 2 according to the RPC method, and the RI distribution image is reconstructed from the sinogram after the standardized projection process by the back projection method.
Next, this RI distribution image is re-projected again considering the above-mentioned absorber distribution to create a sinogram, and this sinogram is again subjected to standardized projection processing based on the RPC method. Let C1 be the sinogram obtained by the first standardized projection and C2 be the sinogram obtained by the second standardized projection, and perform an operation of F = 2-C2 / C1 to calculate F at each point of the sinogram. Find each angle. Thus, a standard correction matrix is obtained. Note that the correction matrix is actually further smoothed and then stored in the memory 3. Since this correction matrix is a standard one for a specific examination site, when the correction matrix is applied to the actual subject, for example, in the correction arithmetic processing unit 4, for example, the myocardial SP
When reconstructing an ECT image, it is corrected according to the center position and size of the myocardium. Then, if the sinogram obtained by normalizing the sinogram obtained for the actual subject by the normalization projection device 2 based on the RPC method is multiplied by the corrected correction matrix by the multiplier 5, the nonuniform absorption is obtained. You can eliminate the error caused by the body.

【The invention's effect】

According to the SPECT image reconstructing apparatus of the present invention, the error due to the nonuniform absorber can be corrected by correcting the projection data that has been subjected to the standardized projection processing by the RPC method with the correction matrix. Therefore, in particular, it is possible to perform simple, highly accurate, and practical absorption correction, which is most suitable for the myocardial SPECT image of the chest with many non-uniform absorbers.

[Brief description of drawings]

The figure is a block diagram of an embodiment of the present invention. 1 ... Data collection memory, 2 ... Standardized projection device, 3 ...
... correction matrix memory, 4 ... correction processing unit, 5
…… Multiplier, 6 …… Image reconstruction processor.

Claims (1)

(57) [Claims] 1. A SPECT image reconstructing apparatus comprising means for performing a standardized projection process on projection data by an RPC method and image reconstructing means by a back projection method, and a standard RI distribution at a predetermined examination site. The first standardized projection data obtained by processing the projection data obtained from the absorber distribution with the standardized projection means and the image reconstructed using the first standardized projection data are projected again. The projection data obtained by processing the projection data again by the standardized projection means
Storage means for storing a correction matrix obtained by obtaining the comparison with the standardized projection data for each point and each angle, and means for correcting the correction matrix according to the state of the actual examination site of the subject. And a means for multiplying the standardized projection data on the actual examination site of the subject to be obtained by the standardized projection means by the corrected correction matrix.